As a method for sealing a semiconductor, a resin-sealing with an epoxy resin is generally used in view of good balance of economical efficiency, productivity and physical properties, and among them, the resin-sealing composed of an o-cresol novolac-type epoxy resin and a phenol-novolac curing agent and an inorganic filler such as silica has been used widely. However, in recent years, with a larger size LSI chip, a thinner/more compact size package, and change of a packaging system or the like, performance required to a sealing material has been changed largely, and sufficient response by a conventional epoxy resin sealing material has become difficult, in respect to humidity resistance, heat resistance, reliability or the like. For example, in heat treatment in soldering, a present problem is generation of crack or peeling of a package accompanied with abrupt vaporization and expansion of absorbed moisture. In particular, with increasing use of lead-free solder in recent years, this problem has become increasingly serious. In addition, use of a bromine compound or an antimony compound, conventionally used as a flame retardant, has been reexamined from environmental problems.
Accordingly, there has been desired a development of an epoxy resin or a curing agent having low moisture absorption, low elastic modulus at soldering temperature and excellent adhesion properties. In addition, there has been desired a development of an epoxy resin or a curing agent difficult in combustion and has excellent flame retardance.
As a curing agent satisfying such requirements, there has been noticed a phenolic resin having a biphenyl skeleton derived from a 4,4′-bismethylbiphenyl compound and phenols (for example, see Patent References 1 and 2). However, an epoxy resin composition obtained by using such a phenolic resin as a curing agent, had a drawback having inferior curing property, as compared with an epoxy resin composition obtained by using a phenolaralkyl resin derived from a 4,4′-xylylene compound and a phenol as a curing agent. Still more, temperature of a kneading roll or a kneader in producing semiconductor sealing materials or the like is equal to or lower than 120° C., and temperature equal to or higher than this makes production of sealing materials difficult because of generation of a problem of viscosity increase or the like, caused by a reaction between an epoxy resin and a curing agent in kneading. Therefore, as a curing agent or an epoxy resin used in this application, one having a softening point of equal to or lower than 100° C., preferably equal to or lower than 80° C. is desirable. On the other hand, it is desired that melt viscosity is low at a molding temperature region of a curing agent or an epoxy resin, in order to maintain melt viscosity low in molding, even when a large quantity of inorganic fillers are compounded, which are essential to be compounded into semiconductor sealing materials. However, a phenolic resin having a biphenyl skeleton, described in the above documents, had a problem that by making average molecular weight smaller to lower melt viscosity, crystallization tends to occur more easily, resulting in abrupt increase in softening point.    Patent Reference 1: JP-A-2000-129092    Patent Reference 2: JP-A-2000-226498